// ImGui GLFW binding with OpenGL3 + shaders
// In this binding, ImTextureID is used to store an OpenGL 'GLuint' texture identifier. Read the FAQ about ImTextureID in imgui.cpp.

// You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
// If you use this binding you'll need to call 4 functions: ImGui_ImplXXXX_Init(), ImGui_ImplXXXX_NewFrame(), ImGui::Render() and ImGui_ImplXXXX_Shutdown().
// If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.
// https://github.com/ocornut/imgui

#include <imgui/imgui.h>

#include <Windows.h>
#include <../depends/include/GL/glew.h>

#include <SpecialK/window.h>

// Data
static INT64        g_Time                   = 0;
static INT64        g_TicksPerSecond         = 0;
static bool         g_MousePressed [3]       = { false, false, false };
static float        g_MouseWheel             = 0.0f;
static GLuint       g_FontTexture            = 0;
static int          g_ShaderHandle           = 0,
                    g_VertHandle             = 0,
                    g_FragHandle             = 0;
static int          g_AttribLocationTex      = 0,
                    g_AttribLocationProjMtx  = 0;
static int          g_AttribLocationPosition = 0,
                    g_AttribLocationUV       = 0,
                    g_AttribLocationColor    = 0;
static unsigned int g_VboHandle              = 0,
                    g_VaoHandle              = 0,
                    g_ElementsHandle         = 0;

// This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
// If text or lines are blurry when integrating ImGui in your engine:
// - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
void
ImGui_ImplGL3_RenderDrawLists (ImDrawData* draw_data)
{
  // Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
  ImGuiIO& io =
    ImGui::GetIO ();

  int fb_width  = (int)(io.DisplaySize.x);// * io.DisplayFramebufferScale.x);
  int fb_height = (int)(io.DisplaySize.y);// * io.DisplayFramebufferScale.y);

  if (fb_width == 0 || fb_height == 0)
    return;

  draw_data->ScaleClipRects (ImVec2 (1.0f, 1.0f));//io.DisplayFramebufferScale);

  // Backup GL state
  GLint     last_program;              glGetIntegerv (GL_CURRENT_PROGRAM,              &last_program);
  GLint     last_texture;              glGetIntegerv (GL_TEXTURE_BINDING_2D,           &last_texture);
  GLint     last_active_texture;       glGetIntegerv (GL_ACTIVE_TEXTURE,               &last_active_texture);
  GLint     last_array_buffer;         glGetIntegerv (GL_ARRAY_BUFFER_BINDING,         &last_array_buffer);
  GLint     last_element_array_buffer; glGetIntegerv (GL_ELEMENT_ARRAY_BUFFER_BINDING, &last_element_array_buffer);
  GLint     last_vertex_array;         glGetIntegerv (GL_VERTEX_ARRAY_BINDING,         &last_vertex_array);
  GLint     last_blend_src;            glGetIntegerv (GL_BLEND_SRC,                    &last_blend_src);
  GLint     last_blend_dst;            glGetIntegerv (GL_BLEND_DST,                    &last_blend_dst);
  GLint     last_blend_equation_rgb;   glGetIntegerv (GL_BLEND_EQUATION_RGB,           &last_blend_equation_rgb);
  GLint     last_blend_equation_alpha; glGetIntegerv (GL_BLEND_EQUATION_ALPHA,         &last_blend_equation_alpha);
  GLint     last_viewport    [4];      glGetIntegerv (GL_VIEWPORT,                      last_viewport);
  GLint     last_scissor_box [4];      glGetIntegerv (GL_SCISSOR_BOX,                   last_scissor_box); 
  GLboolean last_enable_blend        = glIsEnabled   (GL_BLEND);
  GLboolean last_enable_cull_face    = glIsEnabled   (GL_CULL_FACE);
  GLboolean last_enable_depth_test   = glIsEnabled   (GL_DEPTH_TEST);
  GLboolean last_enable_scissor_test = glIsEnabled   (GL_SCISSOR_TEST);

  // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled
  glEnable        (GL_BLEND);
  glBlendEquation (GL_FUNC_ADD);
  glBlendFunc     (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  glDisable       (GL_CULL_FACE);
  glDisable       (GL_DEPTH_TEST);
  glEnable        (GL_SCISSOR_TEST);
  glActiveTexture (GL_TEXTURE0);

  // Setup viewport, orthographic projection matrix
  glViewport ( 0, 0,
              (GLsizei)fb_width, (GLsizei)fb_height );

  const float ortho_projection [4][4] =
  {
      { 2.0f/io.DisplaySize.x, 0.0f,                   0.0f, 0.0f },
      { 0.0f,                  2.0f/-io.DisplaySize.y, 0.0f, 0.0f },
      { 0.0f,                  0.0f,                  -1.0f, 0.0f },
      {-1.0f,                  1.0f,                   0.0f, 1.0f },
  };

  glUseProgram       (g_ShaderHandle);
  glUniform1i        (g_AttribLocationTex, 0);
  glUniformMatrix4fv (g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
  glBindVertexArray  (g_VaoHandle);

  for (int n = 0; n < draw_data->CmdListsCount; n++)
  {
    const ImDrawList* cmd_list = draw_data->CmdLists[n];
    const ImDrawIdx* idx_buffer_offset = 0;

    glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
    glBufferData(GL_ARRAY_BUFFER, (GLsizeiptr)cmd_list->VtxBuffer.Size * sizeof(ImDrawVert), (const GLvoid*)cmd_list->VtxBuffer.Data, GL_STREAM_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, (GLsizeiptr)cmd_list->IdxBuffer.Size * sizeof(ImDrawIdx), (const GLvoid*)cmd_list->IdxBuffer.Data, GL_STREAM_DRAW);

    for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
    {
      const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
      if (pcmd->UserCallback)
      {
        pcmd->UserCallback(cmd_list, pcmd);
      }
      else
      {
        glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
        glScissor((int)pcmd->ClipRect.x, (int)(fb_height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
        glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer_offset);
      }
      idx_buffer_offset += pcmd->ElemCount;
    }
  }

  // Restore modified GL state
  glUseProgram(last_program);
  glActiveTexture(last_active_texture);
  glBindTexture(GL_TEXTURE_2D, last_texture);
  glBindVertexArray(last_vertex_array);
  glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, last_element_array_buffer);
  glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha);
  glBlendFunc(last_blend_src, last_blend_dst);
  if (last_enable_blend) glEnable(GL_BLEND); else glDisable(GL_BLEND);
  if (last_enable_cull_face) glEnable(GL_CULL_FACE); else glDisable(GL_CULL_FACE);
  if (last_enable_depth_test) glEnable(GL_DEPTH_TEST); else glDisable(GL_DEPTH_TEST);
  if (last_enable_scissor_test) glEnable(GL_SCISSOR_TEST); else glDisable(GL_SCISSOR_TEST);
  glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
  glScissor(last_scissor_box[0], last_scissor_box[1], (GLsizei)last_scissor_box[2], (GLsizei)last_scissor_box[3]);
}

static const char*
ImGui_ImplGL3_GetClipboardText (void* user_data)
{
  return nullptr;//return glfwGetClipboardString((GLFWwindow*)user_data);
}

static void
ImGui_ImplGL3_SetClipboardText (void* user_data, const char* text)
{
  //glfwSetClipboardString((GLFWwindow*)user_data, text);
}

bool
ImGui_ImplGL3_CreateFontsTexture (void)
{
  // Build texture atlas
  ImGuiIO& io =
    ImGui::GetIO ();

  extern void
  SK_ImGui_LoadFonts (void);

  SK_ImGui_LoadFonts ();

  unsigned char* pixels;
  int            width, height;

  // Load as RGBA 32-bits (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.
  io.Fonts->GetTexDataAsRGBA32 (&pixels, &width, &height);
  
  // Upload texture to graphics system
  GLint last_texture;

  glGetIntegerv   (GL_TEXTURE_BINDING_2D, &last_texture);
  glGenTextures   (1, &g_FontTexture);
  glBindTexture   (GL_TEXTURE_2D, g_FontTexture);
  glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexImage2D    (GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
  
  // Store our identifier
  io.Fonts->TexID =
    (void *)(intptr_t)g_FontTexture;
  
  // Restore state
  glBindTexture (GL_TEXTURE_2D, last_texture);
  
  return true;
}

bool
ImGui_ImplGlfwGL3_CreateDeviceObjects (void)
{
  // Backup GL state
  GLint last_texture,
        last_array_buffer,
        last_vertex_array;

  glGetIntegerv (GL_TEXTURE_BINDING_2D,   &last_texture);
  glGetIntegerv (GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
  glGetIntegerv (GL_VERTEX_ARRAY_BINDING, &last_vertex_array);

  const GLchar *vertex_shader =
      "#version 330\n"
      "uniform mat4 ProjMtx;\n"
      "in vec2 Position;\n"
      "in vec2 UV;\n"
      "in vec4 Color;\n"
      "out vec2 Frag_UV;\n"
      "out vec4 Frag_Color;\n"
      "void main()\n"
      "{\n"
      "	Frag_UV = UV;\n"
      "	Frag_Color = Color;\n"
      "	gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
      "}\n";

  const GLchar* fragment_shader =
      "#version 330\n"
      "uniform sampler2D Texture;\n"
      "in vec2 Frag_UV;\n"
      "in vec4 Frag_Color;\n"
      "out vec4 Out_Color;\n"
      "void main()\n"
      "{\n"
      "	Out_Color = Frag_Color * texture( Texture, Frag_UV.st);\n"
      "}\n";

  g_ShaderHandle = glCreateProgram ();
  g_VertHandle   = glCreateShader  (GL_VERTEX_SHADER);
  g_FragHandle   = glCreateShader  (GL_FRAGMENT_SHADER);

  glShaderSource  (g_VertHandle, 1, &vertex_shader, 0);
  glShaderSource  (g_FragHandle, 1, &fragment_shader, 0);
  glCompileShader (g_VertHandle);
  glCompileShader (g_FragHandle);
  glAttachShader  (g_ShaderHandle, g_VertHandle);
  glAttachShader  (g_ShaderHandle, g_FragHandle);
  glLinkProgram   (g_ShaderHandle);

  g_AttribLocationTex      = glGetUniformLocation (g_ShaderHandle, "Texture");
  g_AttribLocationProjMtx  = glGetUniformLocation (g_ShaderHandle, "ProjMtx");
  g_AttribLocationPosition = glGetAttribLocation  (g_ShaderHandle, "Position");
  g_AttribLocationUV       = glGetAttribLocation  (g_ShaderHandle, "UV");
  g_AttribLocationColor    = glGetAttribLocation  (g_ShaderHandle, "Color");

  glGenBuffers (1, &g_VboHandle);
  glGenBuffers (1, &g_ElementsHandle);

  glGenVertexArrays (1, &g_VaoHandle);
  glBindVertexArray (g_VaoHandle);
  glBindBuffer      (GL_ARRAY_BUFFER, g_VboHandle);

  glEnableVertexAttribArray (g_AttribLocationPosition);
  glEnableVertexAttribArray (g_AttribLocationUV);
  glEnableVertexAttribArray (g_AttribLocationColor);

#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
  glVertexAttribPointer (g_AttribLocationPosition, 2, GL_FLOAT,         GL_FALSE, sizeof (ImDrawVert), (GLvoid *)OFFSETOF (ImDrawVert, pos));
  glVertexAttribPointer (g_AttribLocationUV,       2, GL_FLOAT,         GL_FALSE, sizeof (ImDrawVert), (GLvoid *)OFFSETOF (ImDrawVert, uv));
  glVertexAttribPointer (g_AttribLocationColor,    4, GL_UNSIGNED_BYTE, GL_TRUE,  sizeof (ImDrawVert), (GLvoid *)OFFSETOF (ImDrawVert, col));
#undef OFFSETOF

  ImGui_ImplGL3_CreateFontsTexture ();

  // Restore modified GL state
  glBindTexture     (GL_TEXTURE_2D,   last_texture);
  glBindBuffer      (GL_ARRAY_BUFFER, last_array_buffer);
  glBindVertexArray (last_vertex_array);

  return true;
}

void
ImGui_ImplGL3_InvalidateDeviceObjects (void)
{
  if (g_VaoHandle)      glDeleteVertexArrays (1, &g_VaoHandle);
  if (g_VboHandle)      glDeleteBuffers      (1, &g_VboHandle);
  if (g_ElementsHandle) glDeleteBuffers      (1, &g_ElementsHandle);

  g_VaoHandle = g_VboHandle = g_ElementsHandle = 0;

  if (g_ShaderHandle && g_VertHandle) glDetachShader (g_ShaderHandle, g_VertHandle);
  if (g_VertHandle)                   glDeleteShader (g_VertHandle);

  g_VertHandle = 0;

  if (g_ShaderHandle && g_FragHandle) glDetachShader (g_ShaderHandle, g_FragHandle);
  if (g_FragHandle)                   glDeleteShader (g_FragHandle);

  g_FragHandle = 0;

  if (g_ShaderHandle) glDeleteProgram (g_ShaderHandle);

  g_ShaderHandle = 0;

  if (g_FontTexture)
  {
    glDeleteTextures (1, &g_FontTexture);
    ImGui::GetIO ().Fonts->TexID = 0;
    g_FontTexture = 0;
  }
}

bool
ImGui_ImplGL3_Init (void)
{
  static bool first = true;

  if (first) {
    if (! QueryPerformanceFrequency ((LARGE_INTEGER *)&g_TicksPerSecond))
      return false;

    if (! QueryPerformanceCounter   ((LARGE_INTEGER *)&g_Time))
      return false;

    first = false;
  }

  //g_Window = window;

  ImGuiIO& io = ImGui::GetIO();
  // Keyboard mapping. ImGui will use those indices to peek into the io.KeyDown[] array that we will update during the application lifetime.
  io.KeyMap [ImGuiKey_Tab]        = VK_TAB;
  io.KeyMap [ImGuiKey_LeftArrow]  = VK_LEFT;
  io.KeyMap [ImGuiKey_RightArrow] = VK_RIGHT;
  io.KeyMap [ImGuiKey_UpArrow]    = VK_UP;
  io.KeyMap [ImGuiKey_DownArrow]  = VK_DOWN;
  io.KeyMap [ImGuiKey_PageUp]     = VK_PRIOR;
  io.KeyMap [ImGuiKey_PageDown]   = VK_NEXT;
  io.KeyMap [ImGuiKey_Home]       = VK_HOME;
  io.KeyMap [ImGuiKey_End]        = VK_END;
  io.KeyMap [ImGuiKey_Delete]     = VK_DELETE;
  io.KeyMap [ImGuiKey_Backspace]  = VK_BACK;
  io.KeyMap [ImGuiKey_Enter]      = VK_RETURN;
  io.KeyMap [ImGuiKey_Escape]     = VK_ESCAPE;
  io.KeyMap [ImGuiKey_A]          = 'A';
  io.KeyMap [ImGuiKey_C]          = 'C';
  io.KeyMap [ImGuiKey_V]          = 'V';
  io.KeyMap [ImGuiKey_X]          = 'X';
  io.KeyMap [ImGuiKey_Y]          = 'Y';
  io.KeyMap [ImGuiKey_Z]          = 'Z';

  io.RenderDrawListsFn  = ImGui_ImplGL3_RenderDrawLists;       // Alternatively you can set this to NULL and call ImGui::GetDrawData() after ImGui::Render() to get the same ImDrawData pointer.
  //io.SetClipboardTextFn = ImGui_ImplGL3_SetClipboardText;
  //io.GetClipboardTextFn = ImGui_ImplGL3_GetClipboardText;
  io.ClipboardUserData  = game_window.hWnd;

  return true;
}

void
ImGui_ImplGL3_Shutdown (void)
{
  ImGui_ImplGL3_InvalidateDeviceObjects ();
  ImGui::Shutdown ();
}

void
SK_ImGui_PollGamepad (void);

void
ImGui_ImplGL3_NewFrame (void)
{
  if (! g_FontTexture)
    ImGui_ImplGlfwGL3_CreateDeviceObjects ();

  ImGuiIO& io =
    ImGui::GetIO ();

  // Setup display size (every frame to accommodate for window resizing)
  int         w,         h;
  int display_w, display_h;

  RECT client;
  GetClientRect (game_window.hWnd, &client);

  w = client.right  - client.left;
  h = client.bottom - client.top;

  display_w = w;
  display_h = h;

  io.DisplaySize             = ImVec2 ((float)w, (float)h);
  io.DisplayFramebufferScale = ImVec2 ((float)w, (float)h);//ImVec2 (w > 0 ? ((float)display_w / w) : 0, h > 0 ? ((float)display_h / h) : 0);

  // Setup time step
  INT64 current_time;

  QueryPerformanceCounter ((LARGE_INTEGER *)&current_time);

  io.DeltaTime = (float)(current_time - g_Time) / g_TicksPerSecond;
  g_Time       =         current_time;

  // Read keyboard modifiers inputs
  io.KeyCtrl   = (GetAsyncKeyState_Original (VK_CONTROL) & 0x8000) != 0;
  io.KeyShift  = (GetAsyncKeyState_Original (VK_SHIFT)   & 0x8000) != 0;
  io.KeyAlt    = (GetAsyncKeyState_Original (VK_MENU)    & 0x8000) != 0;

  io.KeySuper  = false;

  SK_ImGui_PollGamepad ();

  // Start the frame
  ImGui::NewFrame ();
}